X-ray imaging system having improved weather resistance

ABSTRACT

It is an object of the present invention to provide a radiation inspection system, such as an X-ray system, that can operate efficiently even in inclement weather conditions while being highly mobile. Thus the improved inspection system of the present invention is capable of operating in high temperature and corrosive environments and is designed to withstand moisture, dirt and/or dust from the articles of inspection as well.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present invention relies on, for priority, U.S. Provisional PatentApplication No. 60/671,900, entitled “X-Ray System Having ImprovedWeather Resistance”, filed on Apr. 15, 2005.

FIELD OF THE INVENTION

The present invention generally relates to the field of radiant energyimaging systems for detecting concealed objects, and more specificallyto a detection system capable of operating in rugged, intense, and/orinclement weather environments. Specifically, the present invention isan X-ray inspection system having improved weather resistance. Morespecifically, the present invention is designed for use in outdoorvenues and extreme temperatures.

BACKGROUND OF THE INVENTION

The inspection of baggage and/or other cargo at transit points such asairports and shipping ports has become almost universally mandatory.Luggage or cargo can be used for illegal transportation of contrabandsuch as explosives, weapons, narcotics and dangerous chemicals. Thiswarrants a rapid and accurate inspection system for determining thepresence of concealed illegal materials.

X-ray scanning systems are the most widely used detection systems thatprovide for efficient inspection without the need for opening baggage.In conventional X-ray baggage systems, X-ray beams are directed throughbaggage as it is moved on a conveyor belt in a horizontal direction. TheX-rays that have passed through the baggage are then processed fordisplay on a video monitor to provide images of the contents of thebaggage.

In general, conventional X-ray inspection systems work well withinindoor environments, such as at airports. Conventional inspectionsystems, however, are also employed at ports, border crossings andcustoms checkpoints and/or sports venues, where space for housing andstructures are not readily available. Thus, the ability of a system tooperate outdoors becomes an important consideration.

Several components of conventional X-ray baggage systems are readilysusceptible to damage when operating in inclement environments. Forexample, if a baggage inspection system is deployed in maritimeenvironments such as a naval port, it must be able to endure the rigorsof rain, sleet, salt spray and salt fog during operation.

These inclement weather elements could cause structural damage toconventional radiation shielding for the X-rays, thereby rendering thesystem hazardous to operate. Other parts of an X-ray inspection systemthat can be damaged due to moisture, humidity, dust and extremetemperatures, including the X-ray tube assembly and the collimator,which may alter the emission and scattering of X-rays, and the motors.In this case, not only the imaging quality of the system is adverselyaffected, but it also becomes electrically unsafe and unreliable.

Although most baggage inspection systems have a shielded housing for theX-ray tube, this alone is not sufficient to ensure unhinderedfunctioning of the system in adverse weather conditions.

Attempts at improving the functioning of X-ray detection systems havelargely focused on compensating for the effects of environmental factorson the system's detection capability. For example, U.S. Pat. No.5,970,113 discloses a CT scanning system having a radiation source fordirecting radiation through a region and an array of detectors forreceiving radiation from the region while scanning the region and forgenerating detector signals indicative of the received radiation, amethod of compensating for electrical currents that are generated by thedetectors independently of radiation received by the detectors, saidmethod comprising: generating a calibration relationship for the arrayof detectors, said generating comprising: varying the temperature of thearray of detectors, measuring the electrical currents generated by thedetectors as the temperature of the detectors is varied, characterizingthe variation in the electrical currents with temperature, using thevariation in the electrical currents with temperature, generating a setof first detector offset signals to be applied to the detector signalsgenerated while scanning the region; after generating the calibrationrelationship, sensing a first temperature of the array of detectors;measuring a first updated detector offset signal associated with thefirst temperature; scanning the region to generate a detector signal;sensing a second temperature of the array of detectors; using the secondtemperature, the calibration relationship, and the first updateddetector offset signal, adjusting the first updated detector offsetsignal to generate an adjusted detector offset signal such that theadjusted detector offset signal is based on the first updated detectoroffset signal, the second temperature and the calibration relationship;and applying the adjusted detector offset signal to the detector signal.

This abovementioned prior art system, however, does not address thepotential structural and internal damage that a detection system canincur when operated in harsh weather conditions. Conventional prior artbaggage inspection systems are thus presently limited in their abilityto withstand the effects of unfavorable and inclement operatingenvironments.

What is therefore needed is a baggage inspection system that is capableof delivering optimum threat detection performance when operated ininclement weather.

Since dust or moisture on the baggage itself may also harm an inspectionsystem, what is also needed is a baggage inspection system that isdesigned to both withstand inclement weather conditions and remainsubstantially unaffected by the type of baggage being scanned.

What is also needed is a system that is designed for mobility.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a radiationinspection system, such as an X-ray system, that can operate efficientlyeven in inclement weather conditions while being highly mobile. Thus theimproved inspection system of the present invention is capable ofoperating in high temperature and corrosive environments and is designedto withstand moisture, dirt and/or dust from the articles of inspectionas well. The X-ray system can be used to identify any type of item,including bombs, metals, knives, razors, explosives, drugs, narcotics,organic matter, such as plants, seeds, animals, insects, or meatproducts, or any other type of threat or undesirable item.

In accordance with an object of the present invention, one embodiment ofthe X-ray system comprises a conveyor belt system that loops along theexternal body of the x-ray system, instead of on the inside, as withconventional X-ray systems.

In another embodiment, the X-ray system of the present inventionoptionally comprises internal dehumidification devices and externalvacuum-type cleaning devices to remove moisture and dust/dirt from thesystem.

In accordance with still another object of the present invention, theX-ray system comprises temperature regulating devices, such as internalcooling devices such as air conditioning and/or exhaust fans to removeheat generated during operation of the system as well as to cool thesystem from external high temperatures and heaters for warming thesystem in cold environments. The system preferably further comprisescontrols to either heat or cool the system.

It is also an object of the present invention to provide an inspectionsystem that is capable of operating in outdoor weather conditions withminimal protective covering, limited, in one exemplary use, to anoverhead canvas cover.

According to another aspect of the present invention, the inspectionsystem is capable of at dual voltages (110/220 VAC) to comply with powerrequirements in virtually any geography.

In accordance with yet another object of the present invention the X-rayinspection system is portable and can be efficiently transported. Arugged, labeled, removable conveyor casing made up of either stainlesssteel or marine lumber material is provided for the system, which actsas a protective cover when the system is not in use and also when thesystem is to be transported from one place to another. Additionalfixtures, such as fork tubes to facilitate movement using a standardforklift and sling-lift eyelet points to be hooked to the slings of acrane and be airlifted, are also provided that enable ease oftransportation of the inspection system.

An embodiment of the present invention comprises software algorithms toprocess scan data to search the contents of an inspected object, such asbaggage, for targeted material. The system differentiates low atomicnumber (low-Z), medium atomic number (medium-Z) and high atomic number(high-Z) materials by analyzing the size and dual energy transmissionsof the object examined. The thus differentiated regions of the objectare displayed to an operator in the form of a suitably color codedimage.

A yet another embodiment of the present invention comprises software fortraining and testing the X-ray screening operators that randomly insertsfictional threat items such as guns, bombs, or knives into the X-rayimage of the actual item undergoing screening.

In one embodiment, the X-ray imaging system for searching an object forconcealed threats comprises an X-ray source encased in a firstenclosure, a conveyor belt assembly arranged to loop around the externalunderside of said imaging device, an electronics system, such as acomputer, detectors, data acquisition electronics, or power electronics,for controlling the X-ray source, processing data, or managing acquiredimages, and a conveyor belt. The electronic system is encased in atleast one second enclosure. The system also includes a base framephysically integrated with at least one of said first or secondenclosure wherein said base frame comprises a connector for transportingthe system, and a display device for presenting an image of said objectto an operator.

Optionally, the X-ray imaging system further comprises a plurality ofcleaning elements for removing contaminants from said conveyor belt,wherein said cleaning element is at least one of a brush, blower,cleaning pad, or ionizer. The X-ray imaging system further comprises aplurality of heating elements for heating at least one of said X-raysource and electronics system. The X-ray imaging system furthercomprises a sensor for sensing a temperature and a controller whereinsaid controller controls the activation of said X-ray source or saidelectronics and wherein said controller activates said X-ray source orsaid electronics when said temperature sensed by said sensor exceeds apredetermined temperature. Optionally, the connector comprises at leastone of a tube, beam, hook, indentation, or metal projection.

In one embodiment, the X-ray imaging system for searching an object forconcealed threats comprises an X-ray source encased in a firstenclosure, a conveyor belt assembly arranged to loop through the imagingdevice, an electronics system for controlling the X-ray source andconveyor belt, wherein said electronic system is encased in a pluralityof separate enclosures, a base frame physically integrated with at leastone of said first or plurality of separate enclosures wherein said baseframe comprises a connector for transporting the system, and a displaydevice for presenting an image of said object to an operator.

Optionally, the X-ray imaging system further comprises a plurality ofcleaning elements for removing contaminants from said conveyor belt,wherein said cleaning element is at least one of a brush, blower,cleaning pad, or ionizer. The X-ray imaging system further comprises aplurality of heating elements for heating at least one of said X-raysource and electronics system. The X-ray imaging system furthercomprises a sensor for sensing a temperature and a controller whereinsaid controller controls the activation of said X-ray source or saidelectronics and wherein said controller activates said X-ray source orsaid electronics when said temperature sensed by said sensor exceeds apredetermined temperature. Optionally, the connector comprises at leastone of a tube, beam, hook, indentation, or metal projection. Optionally,the X-ray imaging system further comprises removable covers enclosing atleast a portion of said conveyor belt.

The aforementioned and other embodiments of the present shall bedescribed in greater depth in the drawings and detailed descriptionprovided below.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will beappreciated, as they become better understood by reference to thefollowing detailed description when considered in connection with theaccompanying drawings, wherein:

FIG. 1 illustrates the basic structural design of the X-ray imagingsystem having improved weather resistance of the present invention;

FIG. 2 is a schematic diagram illustrating the placement of anenvironmental control system;

FIG. 3 is schematic of the X-ray scanning system of the presentinvention illustrating the external underside of the scanning system;

FIG. 4 depicts another embodiment of the system of present invention;and

FIG. 5 illustrates an exemplary X-ray scan image with embedded fictionalthreat items.

DETAILED DESCRIPTION OF THE INVENTION

The methods and systems described herein are directed towards finding,locating, and confirming threat items and substances. The presentinvention is specifically directed towards an improved inspection systemfor screening objects at security locations. The system of the presentinvention is capable of functioning in inclement weather and ruggedoperating environments while retaining the efficiency of the screeningprocess.

More specifically, the present invention is directed towards an x-raysystem for use in adverse, outdoor weather conditions, with temperaturesranging between 0 to 110° F. (−17 to +43° C.) and is intended to beoperated with minimal protective covering, such as, in one exemplaryuse, to an overhead canvas cover. The cover is used to provideprotection from direct sunlight to the operator's eyes, and to providean anti-glare environment to control unnecessary fatigue.

The system of the present invention further comprises a conveyor beltthat runs along the outside of the x-ray system, compared withconventional X-ray systems, in which the conveyor system runs throughthe inside of the system. This configuration helps keep moisture, dirt,dust, and other foreign elements from the bags out of the system andenables better sealing and protection of the electronics. In anotherembodiment, the conveyor belt entirely runs through the x-ray systemwith cleaning elements positioned inside the x-ray system to keep thesystem substantially clean.

To facilitate rapid deployment, the system is equipped with dual voltagecapability (110/220 VAC) to comply with power requirements in virtuallyany geographical environment.

Although the embodiments are described in the context of a baggageinspection system, it should be evident to persons of ordinary skill inthe art that items other than luggage such as other packages, mail, andcargo-containers, or even processed food stuffs, can also be analyzedand screened or graded and that the descriptions are exemplary and arenot restrictive of the invention.

Although one preferred embodiment of the present invention is describedwith reference to X-ray scanning, one of ordinary skill in the art wouldappreciate that object screening may be performed using any availableradiation imaging technique such as, but not limited to X-rayscattering, infrared imaging, milliwave imaging, RF imaging, radarimaging, holographic imaging, CT imaging, and MRI. Any imaging systemthat has the potential for displaying object detail may be employed.

Reference will now be made in detail to specific embodiments of theinvention. While the invention will be described in conjunction withspecific embodiments, it is not intended to limit the invention to oneembodiment.

FIG. 1 illustrates the basic structural design of the X-ray imagingsystem having improved weather resistance of the present invention.Referring to FIG. 1, X-ray baggage scanning system 100 comprises anenclosure 110 mounted on a base frame 145. To provide structuralreinforcement and a means by which the X-ray imaging system can besafely and reliably moved, the X-ray imaging system further comprisesbeams 130 that connect the enclosure 110 to the base frame 145 and basebeams 125 that extend a substantial portion of the length of the baseframe 145. In one embodiment, the base beams 125 are scissor lifts thatcan be deployed to lower wheels, thereby enabling the system to berolled. Preferably, if the system is to remain stationary, the wheelsare retracted and jacking feet 140 are used to stabilize the system.

It should be appreciated by one of ordinary skill in the art that thebase frame 145 can be solid or comprised of a plurality of connectedpanels. The beams 130 can be L-shaped as depicted in FIG. 1, straight,or any other configuration that provides sufficient structural support.It should be appreciated that the beams 130 are positioned to protectthe belt and conveyor belt from being damaged which could occur, forexample, if the system is rolled against a wall or protusion. Furtherthe base frame 145 comprises connection points 176 that can be used toconnect to hooks, cabling, or other towing mechanisms for airlifting,pushing, pulling, or otherwise moving the system 100. The connectionpoints can comprise a hook, indentation, such as a slot cut, hole, orkey slot, or any type of projection of any material type, such as metalor plastic.

The enclosure 110, base frame 145, beams 130, and base beams 125 arepreferably constructed using regular steel painted with marine gradepaint or stainless steel, enabling the system to function in bothoutdoor as well as industrial environments. In such conditions, apartfrom the weather elements, the system may also be exposed to causticchemicals. This is particularly the case with industrial environmentssuch as the packaged food or meat industry, where the X-ray scanningsystem may be employed for checking food materials for contaminants. Inaddition, any electronics, instrumentation, and display panels, such ascontrol panel 123, are encased in regular steel painted with marinegrade paint or non-corrosive stainless steel paneling 120.

The X-ray baggage scanning system 100 comprises an inspection entrance150 covered by a lead curtain 180. Objects to be inspected are placed onan extended roller surface 185 covered by a conveyor belt 105 whichextends below the extended roller surface 185, downward 175, and overbase roller 115. During operation, the conveyor belt 105 moves forward,through entrance 150 and lead curtain 180, and loops around extendedroller surface [not shown], downward, and over a base roller [notshown]. The conveyor belt 105 moves over the base roller 115, upward,and over extended roller surface 185. It should be appreciated that theconveyor belt 105 can move in either direction.

The conveyor apparatus of the scanning system is in constant andcontinual contact with different types of items under inspection,including baggage. Not all items of inspection, however, are clean, dryand/or ready to be placed into an X-ray system. This is especially trueif the inspection system is operated outdoor, and in particular withinclement weather, or in rugged industrial environments. Thus, dependingupon the location of inspection, the objects of inspection may be dusty,moist, or even contaminated with other environmental factors.

In one embodiment the enclosure 110, toward the base of the structure,comprises a plurality of cleaning elements [not shown] that removewater, dirt, chemicals, and other foreign substances from the conveyorbelt 105 surface in order to prevent the introduction of any substanceswhich could damage the internal detector systems and radiation sources.The cleaning elements can comprise any one of brushes, pads, blowers,dryers, ionizers, or other devices that can substantially remove foreignsubstances from the conveyor belt surface.

FIG. 3 is a block diagram of the X-ray scanning system of the presentinvention, in particular, illustrating the external underside of thescanning system. FIG. 3 depicts X-ray scanning system 310 furtherillustrating the external underside 315 of X-ray unit 310. The conveyorbelt 305 is depicted with a dotted outline. If baggage placed on theconveyor 305 is wet or dirty, the external face of the belt runs on theoutside of the machine to allow it to drip off, and the conveyor belt305 is substantially dry when it comes in contact with and loops backthrough the X-ray unit 310. The system may further comprise at least onevacuum or suction-type cleaning device 320, which are well-known topersons of ordinary skill in the art. Vacuum or suction-type cleaningdevices 320 may thus be employed to draw out the dust on the conveyorbelt 305 as it runs along the outside 315 of the enclosure 310.

One of ordinary skill in the art would appreciate that the enclosure 110encompasses a plurality of detectors and radiation sources [not shown]that expose objects to be inspected to radiation and measures theresulting output. Such detector/radiation source combinations caninclude X-ray transmission and/or scatter detection systems.

Referring to FIG. 2, the system contains an environmental control system230 that ensures the electronic components remain dry and cool. In oneembodiment, the environmental control system 230 comprises an internalhigh-reliability, interlocked dehumidifier to ensure that the electroniccomponents remain dry and cool. In another embodiment, the environmentalcontrol system 230 comprises an internal cooling device that compensatesfor the external heat as well as for the heat generated duringoperation. Optionally, a temperature control device or air conditioningdevice, known to persons of ordinary skill in the art, is interlockedinternally within the system of the present invention. The airconditioning device has sufficient cooling capacity depending upon theload/size of the inspection system and the external temperatures. Inanother embodiment exhaust fans are provided on the chassis of theinspection system that constantly withdraw heat generated in theinternal components of the machine.

In another embodiment, heaters are provided and configured to keepvaried portions of the system warm. Separate heaters are preferablyprovided for the X-ray source and electronics. Also preferably, theelectronics and X-ray source do not turn on until a thresholdtemperature is reached. Therefore, the system further comprises a sensorfor measuring the temperature and a controller for permitting the X-raysource and/or electronics to turn on, upon reaching a predeterminedthreshold temperature, as determined by the sensor, and receiving anactivation signal from an operator.

In another embodiment, a rugged, labeled, removable casing made up ofeither stainless steel or regular steel painted with marine grade paintis provided for the system, which acts as a protective cover for theconveyor belt when the system is not in use and also when the system isto be transported from one place to another. FIG. 4 depicts the system400 of the present invention with the protective casing 405. Theprotective casing 405 is especially useful during transportation of thesystem 400, as it prevents damage to the belts and tunnels of the unitsat the time of loading and unloading. In order to enhance the ease oftransportation, the protective case 405 is designed such that it fitsover the system 400 in two pieces, 410 and 415, in a manner that exposesa set of fork tubes 420, which are provided to facilitate movement usinga standard forklift. In addition or alternatively, threaded, sling-lifteyelet points 425 are provided at the four corners of the casing 405,which enable the system 400 to be hooked to the slings of a crane and beairlifted. Preferably, however, connection points on the base frame areused to connect to hooks, cabling, or other towing mechanisms forairlifting, pushing, pulling, or otherwise moving the system. Theconnection points can comprise a hook, indentation, such as a slot cut,hole, or key slot, or any type of projection of any material type, suchas metal or plastic. It should be appreciated that the presentconfiguration is designed to protect the system from damage duringtransport while still enabling a fast setup of the system. This isachieved by providing casing covers for only the conveyor belt and notencompassing the entire system in a separate casing or crate duringtransport.

In one embodiment, the system depicted in FIG. 4 has a length of 90 to120 inches, a height of 40 to 70 inches, and a width of 50 to 80 inches.The conveyor belt, which is covered by case 405, progresses through atunnel of dimensions 29.53 inches to 21.65 inches at a rate of 30 to 50ft/min. The conveyor is preferably capable of handling a load of 350 to450 lbs. The approximate weight of the system is 4000 to 4500 lbs. Forpower, the system has dual voltage capability (110/220 VAC). The X-rayimage performance has a minimum penetration of 25 mm and a standardpenetration of 29 mm. The X-ray generator is cooled using a sealed oilbath with forced air and has an anode voltage rated at 160KV andoperating at 140KV. The X-ray generator is oriented vertically upward,toward the top-level conveyor belt. It can be stored in temperaturesranging from negative 20 degrees C. to 50 degrees C., operated intemperatures ranging from negative 17 degrees C. to 43 degrees C., andstored or operated in relative humidity ranging from 0 to 100%condensing. The system preferably complies with US military salt sprayrequirements embodied in MIL-STD-810F, which is incorporated herein byreference.

During operation, an item under inspection is first carried along theconveyor belt 105, which, in turn, carries the item into the aperturedefining the entrance 150 to scanning system 100 and through the leadcurtain 180. As the item under inspection passes through the X-scanningsystem 100, an image of the contents of the item is displayed upondisplay screen 185. The generation of X-ray transmission or scatterimages is known to persons of ordinary skill in the art and will not berepeated herein.

Apart from robustness, the present invention focuses on ease ofoperation while maintaining high levels of performance. A preferredembodiment of the system uses preset software algorithms, as known topersons of ordinary skill in the art, to search baggage contents fortargeted material. During the analysis process the size and atomicnumber of the material(s) are examined, and low atomic number (low-Z),medium atomic number (medium-Z) and high atomic number (high-Z) materialare differentiated. This differentiation is presented to the screeningoperator in an easy visual manner, such as by highlighting materialswith different atomic numbers in different colors. The presentapplication incorporates the X-ray analytical systems disclosed in U.S.patent application Ser. No. 10/910,250, entitled “Automatic AlarmResolution for Explosive Detection System”, by reference.

For example, the system is capable of distinguishing between materialsaccording to their inherent characteristics (densities) and thenclassifies for the operator by color. For example, but not limited tosuch color scheme, orange is used for low atomic density, green formedium atomic density and blue for high atomic density material. Mostexplosives are in the low atomic density and thus will be displayed inorange. Other low density materials such as plastics, clothing, andpaper will also be shown in orange. Medium density materials such asaluminum will be displayed in green, while very dense materials likemetals will be shown in blue. In situations where X-rays cannotpenetrate an object due to a combination of thickness and/or density,the image color will be black. This is the case for items such as leadglass vases, and thick metals. Obviously because X-rays are not gettingthrough a black colored item, the bag needs to be opened and inspected,as there is a concealment zone in there.

Another embodiment of the system also provides a reliable andsophisticated method for the training and testing of X-ray screeningpersonnel. This involves using a software package that randomly insertsfictional threat items such as guns, bombs, or knives into the X-rayimage of the actual item undergoing screening. An example of such animage with illusory threat objects is illustrated in FIG. 5. Thisprocess enhances the alertness and threat recognition skills of theoperators, and also provides performance data to supervisors formonitoring the operators' response. This application is detailed in U.S.application Ser. No. 11/343,747, assigned to the applicant of thepresent invention, and is incorporated herein by reference. In anotherembodiment, the present invention outputs data, through a wireless orwired network, to a central station that permits a single user tosupervise the performance of multiple X-ray checkpoints.

In another embodiment, the present invention comprises a control panelthat is protected from water and other contaminants using a clearplastic or glass cover. Furthermore, the control panel can includeenvironmental indicators, such as temperature, humidity, and wind speed.Alternatively, such indicators can be located anywhere else on thesystem.

The above examples are merely illustrative of the many applications ofthe system of present invention. Although only a few embodiments of thepresent invention have been described herein, it should be understoodthat the present invention might be embodied in many other specificforms without departing from the spirit or scope of the invention.Therefore, the present examples and embodiments are to be considered asillustrative and not restrictive, and the invention may be modifiedwithin the scope of the appended claims.

1. An X-ray imaging system for searching an object for an itemcomprising: an X-ray source encased in a first enclosure; a conveyorbelt assembly arranged to loop around the external underside of saidimaging device; an electronics system for controlling the X-ray sourceand conveyor belt, wherein said electronic system is encased in at leastone second enclosure; a base frame physically integrated with at leastone of said first or second enclosure wherein said base frame comprisesa connector for transporting the system; and a display device forpresenting an image of said object to an operator.
 2. The X-ray imagingsystem of claim 1 further comprising a plurality of cleaning elementsfor removing contaminants from said conveyor belt.
 3. The X-ray imagingsystem of claim 2 wherein said cleaning element is at least one of abrush, blower, cleaning pad, or ionizer.
 4. The X-ray imaging system ofclaim 1 further comprising a plurality of heating elements for heatingat least one of said X-ray source and electronics system.
 5. The X-rayimaging system of claim 1 further comprising a sensor for sensing atemperature and a controller wherein said controller controls theactivation of said X-ray source or said electronics.
 6. The X-rayimaging system of claim 5 wherein said controller activates said X-raysource or said electronics when said temperature sensed by said sensorexceeds a predetermined temperature.
 7. The X-ray imaging system ofclaim 1 wherein said connector comprises at least one of a tube, beam,hook, indentation, or metal projection.
 8. The X-ray imaging system ofclaim 1 further comprising removable covers enclosing at least a portionof said conveyor belt.